Um caderno de exercícios chinês, do aluno e do professor

// ═══ Postext Cookbook · Nº 171 · A Chinese exercise book, pupil's and teacher's ═══
// https://postext.dev/en/cookbook/chinese-exercise-book
// Code: MIT · Text: original (CC BY 4.0) · Pictures: generated with diffusion models
// Fonts: Noto Serif SC, Noto Sans SC, LXGW WenKai TC (SIL OFL 1.1) · Needs postext ≥ 1.59.0
import {
  buildDocument, withLoadedFonts, renderPageToCanvas, registerResourceImage,
} from 'https://esm.sh/postext';
import { renderToPdf, decompressWoff2 } from 'https://esm.sh/postext-pdf';

const LANG = 'zh'; // @lang: the language of the frame; the exercise book is Chinese in all
const RECIPE = 'chinese-exercise-book';

// ─── 1 · Design ─────────────────────────────────────────────────────────────
// #region palette: a green exercise book, and the red of the teacher's pen
const palette = {
  ink: '#1f2523', // text: a green-tinted near-black
  green: '#2c7350', // the one accent: section numbers, the subject tab, the squares
  red: '#d0352c', // the teacher's answers
  tint: '#e6f2ea', // the subject tab's ground, the answers box
  rule: '#8fb9a2', // 田字格, the matching dots' lines
  muted: '#68736d', // folios, the series line
  paper: '#ffffff',
};
const col = (id) => ({ hex: palette[id], model: 'hex', paletteId: id });
const colorPalette = [
  ...Object.entries(palette).map(([id, hex]) => ({ id, name: id, value: { hex, model: 'hex' } })),
  { id: 'main-color', name: 'accent (defaults)', value: { hex: palette.green, model: 'hex' } },
];
// #endregion
// 宋 for the text, 黑 for the instructions and labels, 楷 for what the teacher writes.
const [SONG, HEI, KAI] = ['Noto Serif SC', 'Noto Sans SC', 'LXGW WenKai TC'];
const CHARS = 40; // characters per line: 40 × 10.5 pt = 148 mm
const SIZE = 10.5; // pt: 五号, the size of a school book's text

// #region answer: sections 一、二、 that print the pupil's book or the teacher's
// The exercise style is the form; the Markdown holds every word, the points included. The
// same text builds both editions: `edition: 'teacher'` writes each answer into its blank,
// bracket and square in red Kai, rings the right options and draws the matching lines.
const lianxi = {
  id: 'lianxi',
  number: { format: 'simp-chinese-informal', suffix: '、', fontFamily: HEI, color: col('green') },
  instruction: { fontFamily: HEI, bold: false }, // 黑体, not bold: the points stay quiet
  // 选择题: A. B. C. D. in a row, a （　） after the stem for the letter.
  options: { labels: 'alpha-upper', suffix: '.', layout: 'row', bracket: true },
  trueFalse: { look: 'bracket' }, // 判断题: （　） at the end of the line, √ or ×
  blank: { look: 'line', color: col('ink') },
  area: { kind: 'tianzige', color: col('rule') }, // 写话 on 田字格
  match: { color: col('green') },